The present invention relates to a control unit for controlling wireless data transmissions in a mobile communications system provided on board an aircraft, to such a mobile communications system having a control unit of this type, to an associated method for controlling wireless data transmissions in a mobile communications system provided on board an aircraft, and to a computer program for carrying out the method.
To telephone on board an aircraft, mobile communications transmission systems are available which can be used during the flight by cabin crew or passengers. These are mobile communications systems which operate according to the Global System for Mobile Communications (GSM) Standard. With the aid of such a system, the aircraft crew and passengers inside the aircraft cabin can use conventional mobile terminals, such as mobile telephones, personal digital assistants (PDAs), laptops or tablet computers, for the wireless communication. An example of this is the GSM on Aircraft (GSMoA) system (also called GSM on Board (GSMoB) system) standardized by the European Telecommunications Standards Institute (ETSI). For this concept, an on-board GSM base station (also called on-board Base Transceiver Station (BTS)) connected to the terrestrial GSM network via a satellite link is provided in the aircraft. From the point of view of the terrestrial network, the on-board BTS is thus a remote, even if mobile base station. This on-board BTS supplies the on-board radio cell and thus the mobile telephones of the passengers with data from the terrestrial GSM network.
Present-day GSMoA and GSMoB systems provide GSM/GPRS (GPRS: General Packet Radio Service) services, for example, in the GSM1800 and GSM1900 frequency band for passengers and aircraft crew. In the case of GSM1800, a frequency band of 1710 MHz to 1785 MHz is available in the uplink, i.e., for data transmissions from mobile terminals to the on-board BTS, and a frequency band of 1805 MHz to 1880 MHz in the downlink, i.e., for data transmissions from the on-board BTS to the mobile terminals (for GSM1900 accordingly: 1850 MHz to 1910 MHz is available for the uplink and 1930 MHz to 1990 MHz for the downlink). These services are activated in the cruise flight phase from above 3000 meters above ground level.
In order to ensure that the mobile terminals carried (e.g., by passengers) on board connect only with the on-board base station (on-board BTS), establishment of a connection between on-board mobile terminals and terrestrial mobile communications networks (to be more precise, the base stations of the terrestrial mobile communications networks) is prevented. For this purpose, terrestrial mobile communications signals, which are necessary, inter alia, for the establishment of a connection with terrestrial base stations and are emitted from the terrestrial base stations, are masked with the aid of a masking signal (also called a screening signal). This takes places by emitting the masking signal with a predefined transmitting power in the aircraft cabin, in the respective mobile communications bands actively used on the ground, via a special unit located on board (normally called NCU (Network Control Unit) or OBCE (On-Board Control Equipment)). Normally, noise signals or noise-like signals with a bandwidth corresponding to the respective frequency band of the terrestrial mobile communications signals to be masked are used as the masking signal. If terrestrial mobile communications signals in the GSM1800 band are to be masked, the OBCE (NCU) will accordingly generate a noise signal in a frequency range from 1805 MHz to 1880 MHz, in order to mask terrestrial mobile communications signals lying in the GSM1800 downlink frequency band (i.e., signals emitted from terrestrial base stations). If additionally terrestrial mobile communications signals in the GSM900 band are also to be masked, the OBCE (NCU) will also generate in the noise signal a noise component in the GSM900 downlink frequency band (from 935 MHz to 960 MHz).
Put simply, owing to the masking signal covering the entire downlink frequency band relevant for the data transmission, the terrestrial base stations are “invisible” to the on-board mobile terminals.
For the transmission of data on board the aircraft and for establishing communication between the on-board mobile terminals and the on-board GSM base stations, GSM signals are transmitted from the on-board GSM base stations, the on-board BTSs, to the on-board mobile terminals in the downlink direction with a power level lying sufficiently above the masking signal. As a result, on the one hand, communication necessary for the wireless data transmission between the on-board BTS and the on-board mobile terminals is established and, on the other hand, the mobile terminals are prevented from communicating with terrestrial base stations.
The described systems available on board the aircraft reliably provide voice services and data services with low data rate and limited capacity. For example, with GPRS (General Packet Radio Service) maximum data rates of 54.6 kbit/s are achieved. With Enhanced Data Rates for GSM Evolution (EDGE), data rates up to a maximum of 288 kbit/s would be achieved and with the Universal Mobile Telecommunications System (UMTS) as the third generation (3G) mobile communications standard, maximum data rates of 384 kbit/s would be achieved. For multimedia applications, such as fast Internet/Intranet applications, browser-based cabin applications, new types of communication applications (e.g., Skype), audio/video on-demand applications, cabin crew communication and similar broadband applications, in some cases Wireless Local Area Network (WLAN) methods are used. However, WLAN methods do not offer the same possibilities, for example as regards authentication, billing and Quality of Service (QoS), as standard mobile communications methods.